<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 200px;
            height: 200px;

        }
        #a {
            background: #f00;
            float: left;
        }

        #b {
            width: 220px;
            background: #0f0;
            float: left;


        }

        #c {
            background: #00f;
            float: left;


        }
        h1{
            clear: both;
        }
    </style>
</head>

<body>
    <div id="a"></div>
    <div id="b"></div>
    <div id="c"></div>
    <h1>哈哈哈</h1>
</body>

</html>